The present invention relates generally to the field of optical amplifiers and lasers and more particularly to a broad bandwidth optical amplifier and method.
Fiber optics has promised to carry extraordinary amounts of bandwidth. For long haul systems (over 20 miles) the optical signal requires amplification. Until recently this required converting the optical signal to an electrical signal, amplifying the signal and converting it back to an electrical signal. As a result amplification was expensive and limited to the bandwidth of the optical signal. The advent of erbium doped fiber amplifiers (EDFAs) provided an all optical amplifier. The optical signal is directly amplified without conversion to an electrical signal. Unfortunately, EDFAs tend to only amplify a rather narrow range (narrow bandwidth) of optical wavelengths. As a result, other optical amplifiers have been proposed. One of the most promising solutions to the limited bandwidth (wavelength range) is shown in FIG. 1. A pump light, source 20 at a wavelength of 1062 nm is used to pump a P-doped (Phosphorus doped) single mode fiber 22. A plurality of highly reflective (HR) mirrors pairs 24, 26, 28 are strategically spaced about the P-doped single mode fiber 22. Note that the first mirror pair (Bragg gratings) is highly reflective at 1236 nm. The second mirror pair is highly reflective at 1316 nm and the third mirror pair is highly reflective at 1407 nm. As a result the output light 30 has amplified light around 1236 nm, 1316 nm and 1407 nm. A final mirror 32 is highly reflective, at 1062 nm or the pump wavelength. Generally the mirrors 24, 26, 28, 32 are highly reflective near the specified wavelength and are highly transmissive at other wavelengths.
The output light 30 is coupled into a germanium doped single mode fiber 34. The output light 30 acts as a pump for the germanium doped fiber 34. The input communication signal 36 enters the germanium-doped fiber 34 and is amplified. The amplified signal 38 exits through a splitter 40 or other device. While this device is a significant improvement over the EDFAs, amplification of a larger wavelength range is already foreseeable. For instance, the prior art device of FIG. 1 cannot amplify signals in the 700-1000 nm range, which is an important band of wavelengths since it is a highly transmissive part of optical fibers. In addition the prior art systems cannot amplify signals in the gaps between the Stokes amplified lines.
Thus there exist a need for an optical amplifier that can cover a wide range of optical wavelengths in a continuous fashion.